<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
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  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    console.log("'123' == 123",'123' == 123)  // false or true?

    console.log("'' == null", '' == null)    // false or true?

    console.log("'' == 0", '' == 0  )      // false or true?

    console.log("[] == 0", [] == 0  )      // false or true?

    console.log("[] == ''", [] == ''  )     // false or true?

    console.log("[] == ![]", [] == ![] )     // false or true?

    console.log("null == undefined", null == undefined) //  false or true?

    console.log("Number(null)", Number(null))     // 返回什么？

    console.log("Number('')", Number('')  )    // 返回什么？

    console.log("parseInt('')", parseInt(''));    // 返回什么？

    console.log("{ } +1", { } +10  )         // 返回什么？

    let obj = {

      [Symbol.toPrimitive]() {

        return '200';

      },

      valueOf() {

        return 300;

      },

      toString() {

        return 'Hello';

      }

    }

    console.log(Number(obj), 200, '200'); // 这里打印出来是多少？

  </script>
</body>

</html>